【作者】 郭士雄；

【导师】 李国强；

【作者基本信息】 同济大学 ， 结构工程， 2006， 博士

【摘要】 钢结构抗火的目的是使结构在火灾发生后一定的时间内免于倒塌，以保证建筑物内人员安全撤离及消防队有充足时间灭火。由于确定一结构在火灾下的整体稳定性存在相当的难度，目前国内外规范都是通过保证单独构件在火灾下的稳定来确保整体结构在火灾下的安全。最初的钢结构防火设计以基于试验的设计方法为主，由于该方法存在一系列的不足，钢结构防火设计方法逐渐转变为基于计算的设计方法。不管是基于试验的设计方法，还是基于计算的设计方法，都是将构件从整体结构中分离出来，独立的进行抗火设计，通过保证单独构件火灾下的承载能力来确保整体结构在火灾下的安全。随着钢结构抗火研究的发展，国内外越来愈多的研究者对这一方法提出质疑，因为单独构件的受力状态及约束条件与实际结构中的构件有很大不同，整体结构不仅对构件存在约束，而且构件对整体结构会产生反作用，因而以单独构件的火灾反应来代表实际结构中构件的火灾反应，进而据此评估火灾下整体结构的安全与稳定性就会有很大误差。 对火灾下受约束钢构件的研究基本上始于上个世纪90年代中期。在这十多年中，已经取得了一些成果，例如可以采用有限元方法较好的模拟约束钢梁在火灾下的反应、进行参数分析，提出了简化的分析理论，但是在有些方面仍有些不足或研究空白，本文即在前人研究的基础上，对约束钢梁的研究做了一些补充，主要如下： (1)以前约束钢梁的分析理论中，由于模型中截面应力发展在弹性段向塑性段转变时有突变，使梁的变化在弹性段与塑性段不连续，本文提出了连续过渡的应力应变发展理论，解决了这一问题； (2)约束钢梁自身的刚度，对约束钢梁的反应有重要影响，但目前约束钢梁的分析理论中，未能很好的考虑约束钢梁自身刚度的变化。本文根据曲梁的变形特点和虚功原理，分析了约束钢梁自身刚度的变化过程。 (3)以前的研究中，还未见有文献对火灾下约束钢梁局部屈曲的问题进行研究，然而，局部屈曲对梁内轴力变化有很大影响，本文根据弹塑性屈曲理论，对此进行了分析，填补了空白。 (4)以前的研究中，还未见有文献对约束钢梁在降温段的反应进行研究。作者对此进行了理论研究和试验研究。研究表明在降温段约束钢梁内会产生很更多还原

【Abstract】 The aim of fire-resistance design of building structures is to avoid severe damage or collapse during fire attack. Due to the difficulty to determine global stability of a building structure subjected to fire, most Codes and Standards in the world for fire-resistance of structures adopt isolated member capacity checking. By now, there are two fire-resistant design methods of steel structure, the first one is based on experiment, and the second one is based on calculating. However, these two design methods are all for isolated members, not for restrained members in a completed structure. With the progress of recent research on fire-resistance of structures, more and more investigators become doubtful of the effectiveness of these methods, since they have recognized, for example, that the behaviour of a steel beam in a building structure is not the same as that of an isolated beam.In the middle of 1990’s, some researchers began to investigate the behaviour of restrained beams in fire conditions. By now, the behaviour of restrained steel beams can be well simulated by FE method, and some theoretical methods have been presented, but there are still some problems needing to be investigated. In this paper, some of the problems are studied, as listed below:(1) In the previous theories of restrained steel beams, because the stress distribution in the model changes abruptly when it yields, the behaviour of restrained beams is not continuous when it changes from elastic to plastic. In this paper, a continuous development model of stress and strain is presented, through which the above problem is solved.(2) The stiffness of beams, which has not been properly studied in the previous researches, makes an important role on the behaviour of restrained steel beams. In this paper, based on the behaviour of a curved beam, the change of the stiffness of restrained steel beams is studied.(3) In fire conditions, local buckling in restrained steel beams may occur, but it has not been studied by previous researchers. In this paper, local buckling of restrained steel beams is investigated, according to elastic-plastic buckling theory.(4) By now, the behaviour of restrained steel beams during cooling has not been investigated. In this paper, this problem is studied through theoretical analysis and experiment. It is shown that tremendous axial tensile force can be induced in restrained steel beam during cooling.(5) In the current design method for beam-to-column connection, the axial tensile force in restrained steel beams is not taken into account, which may lead to the更多还原